Lubrication fluid in a vehicle gearbox may take a long time to warm up during a warm up phase and/or under cold ambient conditions. Heat may be generated through torque losses in the moving parts of the gearbox and friction (churning) losses in the lubrication fluid. This heat, however, tends to dissipate when the lubrication fluid contacts the housing of the gearbox. When the lubrication fluid is heated, a resulting reduction in viscosity may reduce the increased torque losses and friction losses that occur under cold ambient conditions. By lowering the torque and friction losses an improvement in fuel economy may be obtained.
Torque losses in a gearbox are load-dependent losses that occur when a load is transferred through the gears, shafts, bearings, or other moving parts. Friction losses in a gearbox are no-load losses that may occur without any load being transferred. The friction losses are due to the rotation of the gears, shafts, bearings, or other moving parts in the lubrication fluid. Friction losses are affected by lubrication fluid level, viscosity of the lubrication fluid, and rotational speed of the moving parts in the gearbox. Under cold conditions the thermal mass of the gearbox housing may be much larger than the thermal mass of the lubrication fluid resulting in increased periods of time to heat the lubrication fluid to a desired temperature.